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    Mark Chapline's Avatar
    Mark Chapline Posts: 2, Reputation: 1
    New Member
     
    #1

    Jan 25, 2009, 11:15 AM
    208 single phase vs 208 3 phase
    How can you have the same 208 voltage at 2 pole single phase
    And 208 voltage 3 phase, when there is an additional (3rd) wire.
    Please help.:confused:
    pelle's Avatar
    pelle Posts: 96, Reputation: 0
    Junior Member
     
    #2

    Jan 25, 2009, 04:38 PM

    In this area 120 208 voltage is all multiphase. Usually find it in large apartment houses or downtown area. Where there are 3 transformers. This allows a lot of apts to be run off the transformers and load to be balanced. The voltage comes from how electric is generated and how the phase would be drawn off the transformers.
    For example:
    The apartments are 120 208 using 3 wires 2 hot and one neutral.. you could also pull 120 208 4 wire off this bank with 3 hot and 1 neutral wire. The apt ould uses 2 of the 3 transformers and the for 3 phase all of the transformers are used.
    MarkwithaK's Avatar
    MarkwithaK Posts: 955, Reputation: 107
    Senior Member
     
    #3

    Jan 25, 2009, 04:49 PM
    Quote Originally Posted by Mark Chapline View Post
    how can you have the same 208 voltage at 2 pole single phase
    and 208 voltage 3 phase, when there is an additional (3rd) wire.
    please help.:confused:
    Simplest answer is that the conductors are out of phase not all 3 conductors are hitting at the same time at the load.
    stanfortyman's Avatar
    stanfortyman Posts: 5,598, Reputation: 279
    Electrical & Lighting Expert
     
    #4

    Jan 25, 2009, 05:53 PM
    The simplest answer is really that the voltage is measured across only two conductors at a time.

    Single phase is two wires, A & B. Measured: A-B
    Three phase is three conductors, A, B & C. Measured: A-B, A-C, B-C
    Mark Chapline's Avatar
    Mark Chapline Posts: 2, Reputation: 1
    New Member
     
    #5

    Jan 26, 2009, 08:48 AM
    Quote Originally Posted by MarkwithaK View Post
    Simplest answer is that the conductors are out of phase not all 3 conductors are hitting at the same time at the load.
    Hurray for that answer.
    As I go through this site many answers are loaded with jargon. Your simple answer helped me to understand those long explanations.
    Thanks...
    MarkwithaK's Avatar
    MarkwithaK Posts: 955, Reputation: 107
    Senior Member
     
    #6

    Jan 26, 2009, 09:41 PM

    Glad I could help. I work on a lot of 3-phase compressors and when I first started I didn't fully understand it either.

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